Traveling wave oscillators



Nov. 4, 1958 E. c. DENcH TRAVELING WAVE oscILLAToRs 2 Sheets-Sheet 1 Filed Dec. 30, 1955 L OAD EDWARD C. DEA/CH ATTORNEY Nov. 4, 1958 A E. c. DENcH 2,859,380

TRAVELING WVE OSCILLATORS g3 /72 7 Z5 fo" /NVENTO/ 77762 5 EDWARD C. DEA/CH ATTORNEY United States Patent f TRAVELING WAVE GSCILLATGRS Edward C. Dench, Needham, Mass., assignor to Raytheon Manufacturing Company, Waltham, Mass., a corporationof Delaware Application December 30, 1953, Serial No. 401,340 v2 Claims. (Cl. S15-39.3)

This invention relates to oscillating tubes of the travcling wave type which may be connected either singly or in parallel.

Linear traveling wave tubes are known which comprise an electron gun at one end of said tube, an electron collecting electrode at the other end thereof, and an elongated periodic slow wave propagating structure or delay line, such as a helix, a strapped vane network or an interdigital delay line,` which is adapted to transmit high-frequency energy with a velocity comparable to the velocity of the electron stream. The electrons are projected the vicinity of the periodic delay structure so that high-frequency energy is transferred from the electron stream to the wave propagating along the periodic structure. The energy generated in such tubes may be coupled from said periodicA structure by way of an output coupling means.

In order to obtain sufficient energy interaction, such tubes are usually relatively long and, hence, require an axial magnetic eld to prevent dispersion of the electron beam as it traverses the periodic structure.,

If high beam currents can be maintained in a traveling wave oscillator of the type described, -the gain perV unit length of tube is relatively high and the length of tube necessary for effective production of oscillations may be decreased considerably. If a tube of suciently short length may be used, the axial focusing magnetic field may be eliminated with a consequent saving in size, weight and cost. The above conditions may be attained, in 'accordance with this invention, by connecting a plurality of such traveling wave oscillators in parallel. Furthermore, by connecting the output coupling means of the various traveling wave tubes in parallel, large amounts of power may be derived with comparatively low power tubes, thereby obviating the need for highpower tubes which, because of such factors as external coolingand specially designed cathodes, are relatively diicult and expensive to realize in practice.

If an infinite number of said traveling wave oscillatorswere to be connected radially in shunt, a resulting cylindrical tube would be obtained, comprising a continuous cathode or electron source, a centrally positioned collector electrode and some form of radial periodic transmission line. If the periodic delay line were of the type shown in the application for United States Letters Patent of E. C. Dench, Serial No. 255,499, filed November' 8, 1951, now U. S. Letters Patent No. 2,809,328, issued October 8, 1957, and consisting of a plurality of spaced vanes or paddles depending from a f solid backing member, the developed periodic structure lbecomes a series of coaxially arranged annular members which may depend from a wall of the tube envelope. The resulting cylindrical tube is preferable to a linear tube inasmuchv symmetrical.

Cylindrical traveling wave oscillators have been developed'whose operation depends upon the interaction between an electron beam and one of the space haras it is more compact and tube includes an arcuate periodic delay structure surrounding and concentrically arranged with respect to a cylindrical negative electrode, thus forming an arcuate interaction space. A heated cathode positioned adjacent the sole serves as a source of electrons. Under the combined influence of properly adjusted crossed electric and magnetic elds, these electrons are caused to encircle the interaction space and eventually impinge upon an electron collecting electrodef While such tubes are quite efficient and satisfactory in operation, they require a rather large and heavy magnet assembly in order to permit the electrons to travel in a circular pathY about the arcuate interaction space. It is often desirable, as in the case of airborne equipment, to reduce the size and weight of an oscillator to a minimum. Since magnets of sufficient flux density for use with high-frequency traveling wave oscillators are bulky and heavy, a cylindrical tube capable of operation in the absence of a magnetic field is highly desirable.

Furthermore, since it is often diicult to maintain the eld strength of a permanent magnet uniform over a period o-f time, a traveling wave tube requiring no magnetic eld will have more stable operating char-' acteristics than one including a magnetic field producing means, all other things being equal.

ln addition, where high powerV traveling wave tubes are required, a relatively large cathode is desirable. In prior vtraveling wave oscillator tubes, the cathodes have been comparatively small and limit the amount of power which the tubes are 'capable of supplying.

In one embodimentof traveling wave oscillator tube of the subject invention, the traveling wave V*tube includes an annular cathode mounted within a substantially cylindrical envelope adjacent the circumferential wall of said envelope. The latterV includes a pair of spaced end plates sealed to said wall. A-collector electrode is centrally positioned within the tube envelope and serves to collect the electrons emitted from the surrounding cathode. interposed between the cathode and the collector electrode is aV periodic anode delay structure, consisting of a plurality of spaced, concentrically arranged, annular members depending from oppositely positioned portions of the. tube envelope. The radially directed electron beam passes adjacent this periodic structure and interaction between the beam and the proper spatial harmonic ofthe R. F. field associatedv with the periodicstructure results in the generation rof oscillations. In order to permit the electrons leaving the cathode to obtain a substantially uniform velocity before passing by the periodic anode structure, a positive accelerating electrode is positioned adjacent said cathode.

An output may bederived from the traveling wave oscillator by means of an annular slot in one of the end Walls of the envelopepositioned between any two adjacent annular members near the cathode. Any highfrequency transmission line bounding 'said annular Vslot can be used for coupling the oscillations generated into an external load.

In another embodiment, the cathode and collector electrode are reversed from the position just described so that the cathode is located along the axis of theV The traveling wave oscillator tubes already described may be modified by forming the periodic anode delay line y Patented' Nov.'4, i958 in the formof a series of concentric, annularly arranged sets ofinterdgital members,.each set including alternately disposed members extending, respectively, from oppositely disposed portions of the tube envelope. Each set of the interdigital.v members overlaps the. other set without :.ex. tending all thezway tosthe oppositeportion of the-tube. envelope. electron .beamand the` R. F. wave associated withxthe periodic interdigitalv line,- the overlapping; portions ofi the annular members contain radially-aligned apertures at various angularpositions. The:electrons from the cathode then pass :through the various; apertures as a plurality of radially-directed-beams on their way tothe collector. electrode;l

Since no Vmagnetic eld isrequired .ineither two., embodiments of traveling wave oscillators subject invention, tubesvof comparatively light weight and smaller bulk are obtainable,` and undesirable effects of variations in magneticzfield strength vontube operating characteristics are eliminated. Because of.'the:relatively large cathode obtainedin theembodi'ment havingthe circumferentialcathode, largerfamounts of power may be obtained 'for a given size tubelthan from thetraveling wave oscillatorsof'the prior art. Either of theembodiments shown is of compact, symmetrical construction and Vmay be readily manufactured and reproduced.

Other and further objects and advantages ofethis invention-.will-becomerapparent as the description :thereof progresses, reference being had to the accompanying drawingsv :wherein:

Fig; l is a schematic view of a parallel arrangement of -traveling wave .oscillator tubes;

Fig. 2 is a view showing one form of traveling wave oscillator'tube embodying the subject invention;

Fig. 3 is a View showing an alternative form of traveling Wave oscillator tube embodying the subject invention;

Fig. 4 is a cross-sectional view of a modification of the tube of Fig. 2 having an interdigital periodic anode structure; and

Fig. 5 is a cross-sectional view of the tube vof Fig. 4 taken along line 5 5 of Fig. 4.

In the various figures of the drawing, corresponding elements will be designated by like reference numerals.

Referring to Fig. l, a plurality of radially-disposed traveling wave oscillatorsl are shown schematically, each comprisinga cathode or electron source 11, an electron collecting electrode 12 and a periodic transmission delay line 14 which may, for example, be a helix. The electron1beam 15 yfrom cathode 11 interacts with the, R. FI ieldV alongrthev periodic line 14 to generate energy which travels along. the periodic line in a direction opposite to the direction of movement of the electrons.

of the of the The energy is removed from the end of the periodic line.

remote from the collector electrode by outputzcoupling means 17, indicated by an arrow, while the opposite end of the delay line isterminated by an electrical attenuating means,v such as shown and described in the aforesaid copending application, Serial No. 357,824, and indicated schematically by the cross-hatching 19. The outputs of the tubes are connected in parallel and appliedby way of any suitable -transmission lines 18 to a common load 20 Referringnow to Fig. 2, the traveling wave oscillator tube 10 includesa cylindrical envelope 22 havingacircumferential wall portion 23- joined to a pair of flat, oppositely-.disposed.annular end plates 24 and 25.V An electrically conductive collector electrode 12 is centrally located inv the tube and is xedly mounted to one end plate 25, as shown in Fig. 2. This collector electrode is preferablyitubular in :orden to permit the insertion of a uid cooling conduit27, although a solid collector may be used,- especially in:,low power tubes. An; annular cathode' 11, indirectly, heated by a suitableheater; 28 wound about thefperiphery ofthe cathode, is insulatedly. mounted with respect tothe, circumferential: wall: 23'.- of

To permit .proper interactionibetween: the;

inward, as clearly shown in Fig.I 2, although, in some instances, it may be planar. An external electrical .conf

nection for the cathode and heaters is providedbycmeans of corresponding lead-in conductors 36-38 insulated from wall 23 by means of glass'beadsf39. Av pair1of focusing electrodes 40 and 41 are positioned adjacent to cathode 11. rfhese electrodes may have the same curvature as the cathode so as to form, in effect, an extension ot the cathode. In many instances, however, the inner surface of the focusing electrodes maybe atfrather than convex. The focusing electrodes in practice .may beef maintained at a potential somewhat negative with respect; to the cathode. The presence of the focusing electrodes and the concavity of the cathode emitting surface com:A

bine not only to direct or focus the electron beam radially; inward but also to cause slight divergence of the-beam."V as it progresses toward the collector.

A pairof accelerating electrodes -44vand 4S, one adjacent each endof'the cathode assembly, are mountedf by support rods 47 affixed, in the same manneras thev cathode, to respective end plates 24 and 255 These accelerating-electrodes are maintained positive with respectv to the cathode. The electrical connections to the ac-H celerating 'electrodes and focusing electrodes, like `those. tothe cathode. and-heater, are made through lead-in; conductors 48-51 passing through beaded aperturesin the wall 23 of the tube envelope.

The periodic energy propagating meansfor the vtravel-- ing wave tube is positioned between the electron gun;r assembly and the collector electrode. Because'of thetsymmetrical construction of the tube, a pair of oppositely disposed periodic transmission delay linesor structures 14.@-

and 14 may be providedv to enhance the;interactionbe.;.

tween-the electron beam-and the-periodic line.t The ,ftuberf may, however, operate with a single periodic structure 14: These periodicv anode delay structures each compriserat plurality of coaxially arranged annular electrically con;, ductive members or vanes 78` depending from end, plat e's much as the spacing may be progressively changedv in: eitherfdirection along the periodic line..

The periodic anode delay lines 14 and 14 areelec.- trically interconnected and, being apart of'the tubef envelope, are obviously at thesamevunidirectional current potential as the tube envelope. The periodic anode may be maintained at a potential positive withrespecta to the cathode by means of a connection 57 attached to some point on the tube envelope. As shown in Fig.- 2, collector electrode 12 is electrically a part of theperiodicanode line and, therefore, is at the same unidirectional potential. Alternatively, the collector may be insulated from the periodic anode line and maintained at atleten-.- tial somewhat less positive than the anode whereslightly greater efficiencies are required.

Energy is taken from the -tube through an annular coupling slot 60 -formed in wall 24 of the tube envelope.A

cathode. Since this coupling slot is preferably reentranny.

the portion 24 ofV Wall 24 bounded byztheA slot is sep-r arate from the outer portion of the wall. In this casca mechanical support forthe inner portiony 24I isA furnished by meansof the collector electrode 12which is attached to the underside thereof. If less coupling can be tolerated, the slot may be interrupted at various points in order to permit the portion Z4 of wall 24 to remain integral with the remainder of wall 24. In this way, no mechanical support need be furnished by the collector electrode. To confine the energy emanating from slot 60, an output coupling means 17 is provided in the form of a coaxial line 62, including .an inner conductor 63 and outer conductor 64 attached to the tube envelope. The outer conductor 64 is attached to wall 24 adjacent to and externally of the aperture, as shown in Fig. 2. The inner conductor 63 is fixedly attached to the inner portion 24 of wall 24. The size of the inner conductor depends upon the value of coaxial line impedance desired. To provide proper impedance matching between the travcling wave oscillator and the external load, not shown, over a wide -band of operating frequencies, the coaxial line may be tapered in a manner shown in Fig. 2. A vacuum seal is provided by means of a dielectric bead 65, such as glass, inserted within coaxial line 62, as shown in Fig. 2.

The tube shown in Fig. 3 differs essentially from that shown in Fig. 2 in that the cathode and collector electrodes are reversed so that the electron beam travels radially outward instead of toward the center of the tube. The construction of the tube of Fig. 3 is somewhat simplified inasmuch as the circumferential wall 23 of the tube envelope may serve as the electron collecting electrode. The cathode 11 is centrally mounted within the tube envelope and is preferably concave as viewed from the circumferential wall 23. The cathode contains a longitudinal aperture 13 extending part way through the cathode for receiving one end of a tubular metallic supporting member 68. The aforesaid one end of member 68 is connected, as by welding, to the inner periphery of cathode 11 while the other end, which may be enlarged to provide better mechanical support, is sealed to an electrically insulating element 21 which, in turn, is secured to the end plate 25 of the tube envelope adjacent an aperture therein through which the supporting member and insulating element pass. The cathode is connected to an appropriate source of unidirectional potential by means of a lead 36 electrically connected to the enlarged end of cathode supporting member 68. The cathode heater 2S is inserted within. the bore in supporting member 68 and a vacuum is maintained by means of a glass or ceramic bead 69 through which the heater wire passes. Cathode 11 may be provided with integral end shields 11 at each end thereof which serve not only to minimize emission on the longitudinal axis of the cathode but also as support means for the focusing electrodes 40 and 41. The latter, except for size and method of mounting, are similar to those used in the tube of Fig. 2. The accelerating electrodes 44 and 45 are arranged adjacent to and concentric with said cathode, in like fashion to those of Fig. 2, and may be supported from the corresponding end plates 24 and 25 of the tube by electrically insulating supports 47.

Since the wave energy in the traveling wave oscillator travels in a direction opposite to that of the electron beam, a reversal of the direction of propagation of the electrons will result in energy traveling along the periodic anode network 14 toward the axis of the tube. The annular energy coupling slot 60 in end plate 24 forming a part of output coupling means 17, is, therefore, located between two adjacent annular members 58 near the center of the tube, instead of near the circumferential wall of the tube, as in the case of Fig. 2. With the tube of Fig. 3, therefore, a smaller output coupling means may suffice than in the case of the tube of Fig. 2. This provides for a further simplification in construction of the traveling Wave oscillator.

As pointed out in connection with Fig. 2, unless the apertured slot 60 in the tube of Fig. 3 is made discontinuous in order to maintain the central portion 24 of Y As shown in Figs. 4 and 5, the interdigital structure comprises a first set of concentrically arranged annular members 58a aixed vto and depending from -end plate 24 of the tube envelope. Attached to and extending perpendicularly from the opposite end plate 25 is a second set of coaxially arranged annular members 58h which are interspersed between the Various members of said first set. The free ends of the two sets of members overlap. The overlapping regions of the members' contain a number of apertures 70, depending upon the number of electron beams 15 desired. The apertures in the various members are radially aligned, as shown in Fig. 5, so that the electron beam may readily pass from cathode 11 to collector'electrode 12.

The electron beam, in passing through the apertures in the overlapping members, reacts with the R. F. field associated with the periodic interdigital structure to produce oscillatory energy which may be coupled from the tube by output coupling means 17 including annular coupling slot 60 and a wave guide 72 whose wall 73 lies adjacent to and externally of the annular slot. The wave guide may be provided with a microwave window 75 which maintains a vacuum-tight seal for the tube while, at the same time, being transparent to microwave energy.

A wave guide or coaxial output line may be used alter natively as output coupling means in any of the embodiments of this invention. In fact, the invention is not limited to any particular type of such output deriving means.

It is, of course, possible to utilize an interdigital periodic anode structure of the type Ishown in Figs. 4 and f5 in a tube having a centrally positioned cathode, such as that of Fig. 3.

This invention is not limited to the particular details of construction, materials and processes described, as many equivalents will suggest themselves to those skilled in the art. It is, accordingly, desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

l. In combination, a plurality of self-excited oscillating electron discharge devices each comprising a source of electrons, a two-ended, nonresonant delay network structure producing in the region adjacent thereto fields of electromagnetic wave energy being propagated, each device including means for directing electrons from the corresponding source in energy-exchanging relation only with said fields of wave energy in the corresponding device, the end of each of said delay structures toward which electrons move being provided with electrical attenuating means for substantially preventing reflection of energy therefrom, the end of each of said delay structures away from which electrons move being provided with output deriving means, an output utilization means, and means for connecting the output coupling means of each of said devices to said output utilization means.

2. In combination, a plurality of self-excited oscillating electron discharge devices each comprising a source of electrons, a two-ended, nonresonant delay network structure producing in the region adjacent thereto fields of electromagnetic wave energy being propagated, each device including means for directing electrons from the corresponding source in energy-exchanging relation only with said fields of wave energy in the corresponding device, the end of leach of said delay structures toward which .electrons move being provided with electrical `attenuating means Vfor substantially preventing reflection of--energy therefrom, .the'end of each of said delay structures away from which electrons move being provided with output deriving means, and means for connecting the -foutputrcoupling means of each of said devices in parallel.

' References Cited in the leof this patent UNITED STATES PATENTS 2,245,627 Varian June 17, 1941 3 Skellett Sept. 10, 1946 Kircher Sept. 17, 1946 Maggio Feb. 24, 1948 Glinzton Feb. l, 1949 Bruck Nov. 11, 1952 Brown Mar. 23, 1954 Brown et al. Iune 15, 1954 Jonker Apr. 16, 1957 

